Abrading means



Jam 1.8, 1944. J L H 2,33%,270

ABRADINQG MEANS File d Nov. 28, 1940 e Sheets-Sheet 1 JOSEPH 7. KELLEHEE INVEN TOR.

Jan. 18, 1944. J. 'r. KEl LEHER 2,339,270

gpRApm'e MEANS Filed Nov. '28, 1940 6 Sheets-Sheet 2 INVENTOR. JOSEPH 7- KELLEHEE 6 Sheets-Sheet 3 INVENTOR.

JOSEPH TKELLEl-(EE BY v/m 7T AT RNEY.

Jan. 18, I944. .1. T. KELLEHER 2,339,270

ABRADING MEANS Filed Nov. 28, 1940 's Sheets-Sheet e LL////l/////I///////////////////////// .4 g 'INVENTOR.

JOSEPH T KELLEHEE Patented Jan. 18, 1944 Joseph T. Kellelier, Wakefield, Mass.,.assignor of one-half to American Optical Company, South,-

bridge, Mass, a voluntary association of Massachusetts, and one-half to Neveroil Bearing Company, Wakefield, Mass., a corporation of Massachusetts Application November 28, 1940, Serial No. 367,612

I Claims.

This invention relates to improvements in abrading tools and has particular reference to novelmeans and methods of making abrasive charged tools.

One of the principal objects of the invention is to provide an improved abrasive charged tool 7 and method of making the same-whereby the particles of abrasive. will be' substantially 1miformly distributed throughout the eifective body portion of the tool and the said bonding will have a deisrable resistance to wear and yet Possess a integrally or mechanically bonded with each other.

Another object is to provide improved means and method of forming abrading tools of the above character which will be less expensive and more durable and practical for use.

holdingaction on said abrasive particles which will'tend-to insure their performing the full extent of their usefulness from the tool.

prior to becoming dislodged Another object is to provide novel means and method of forming an abrading tool with a main eifective body portion comprising a mixture of particles of abrasive and particles of metal normally having non-solder'able characteristics heat joined to provide a supp'ort for said abrasive particles and to provide novel means and method by ticles of abrasive-in position thereon until they.

perform. substantially to the full extent of their usefulness with the said supporting metal tend- Other objects and advantages ofthe invention will become apparent from the following description taken in connection with the accompanying drawings and it will be apparent that many changes may be made in the details of construction. arrangement of parts and steps of the processes or methods'shown and described without departing from the spirit of the invention a expressed in the accompanying claims. The invention. therefore, is not intended to be limited to the exact details. arrangement and methods mg to keep pace with the wear of said abrasiveparticles so as to cause the cutting edges thereof to remain exposed during the use of the tool.

Another object is to provide an abrading toolformed of a metal composition of the above nature with means by which the said tool may be easily fitted and attached toan auxiliary support.

Another object is to provid anovel method of forming an abrading tool of a metallic compo sition of the above nature by hardeningsaid tool to a controlled degree of hardness whereby the extent of usefulness of th tool may be greatly increased.

Another object is to provide a novel method 0% otherwise mechanically connected toan auxiliary support.

solderable metal and a portion of solderabie metal providing an abradin'g tool of the'above nature with'a portion thereon which may be soldered or shown and described as the preferred forms only have been given by way of illustration.

Referring to the drawings:

Fig. I is a top plan view of a tool embodying the invention; r

Fig. 11 is a sectional view taken as on line lI-'II of Fig. I;

Fig. III is' a plan view of a part of the tool illustrated in Fig. II which functions as the means by which the abrading' portion of the tool may be fitted and detachably secured to an auxiliary supp Fig. IV is a side elevation of the portion illustrated in Fig. 111; s

Fig. V is a diagrammatic fragmentary sectional view illustrating a step of the process of manufacture;

Fig. VI is a view generally similar to .Fig. V

illustrating a further step in the process of manufacture;

Fig. VII is a fragmentary side elevation shown partially in section ofa press used in the p o ofmanufacture:

sulting from the steps of the process illustrated in Figs. VIII through XII Fig. XIV is a diagrammatic sectional view of a 'fumace illustrating astep in the process of manufacture of the tools of Figs. I, II and XIII;

' Fig. XV is a diagrammatic sectional-view illustrating' a further step in the process of manufacture;

Fig. XVI is a diagrammatic sectional view of another modified form of furnace arrangement.

faces.

The invention, in this particular instance, relates to the forming of interchangeable abrading tools for use with machines for abrading lenses. Such tools are adapted to be held by an auxiliary support-by which they are secured to the abrading machine. Such tools are formed of particles of abrasive supported by a sintered. mixture of metal functioning as means for supporting the abrasive particles during the abrading operation.

One of the main features of the invention is to provide an abrading tool which will have maximum eiliciency and durability to produce the greatest amount of abraded surfaces with a single tool. The tool must be of such a nature as to support the particles of abrasive until they perform the major extent of their usefulness prior to their being dislodged from the supporting means and the supporting means must be of such a nature as to substantially keep pace with the wear of the abrasive particles so as to cause the cutting edges thereof to remain exposed to most efficiently perform their abrading characteristics and means must be provided whereby the tools may be quickly and easily attached to 'or removed from the auxiliary support. These, and other objects of the invention, particularly that of providing a simple and economical method of forming the tools, are the essence of the present invention.

Referring more particularly to the drawings wherein like characters of reference designate like parts throughout the several views the preferred form of tool, as shown in Figs. Ian'd II,

comprises a main effective abrading portion I formed of a mixture of particles of .abrasive such as crushed diamonds, sapphires, corundum or other suitable abrasive means and particles of metal bonded together by a sintering process. The main efiective abrading portion I of the tool has an outer surface 2 of a preformed desired contour shapewhich will generate the various surface curvatures desired on the lenses or articles to be ground thereby. This main effective abrading portion 2 is of a controlled thickness having an inner surface 8 shaped to engage a contiguous surface of a backing support t formed mainly of sintered metallic particles preferably of a similar characteristic as the metallic particles functioning as a bonding means for the abrasive particles of the effective abrading portion of the tool or of any desirable metallic particles which will bond with the metallic particles which support the abrasive means. It is particularly pointed out that the eifective abrading portion of the tool I has an outer portion 5 which is thicker than its adjacent inner portion 6. The purpose of this arrangement is to provide a greater amount of abrasive charged material throughout the portion 5 which is used in generating concaved sur- The reason for this is that more concaved surfaces are generated than convex surfaces and by forming the portion of the tool 5 thicker the said tool has a more balanced general use in forming both the concave and convex surfaces;

that is, one portion for forming one of said sur-' faces is so balanced that it will not spend its extent of usefulness ahead of the other portion so that the tool thereby has a greater range of general use. This is controlled by the particular shape of the inner surface 3 of the tool as illustrated in Fig. II. In orderto provide the effective abrading portion of the tool with maximum curve, generating efllciency and in order &

aaeaare to cause the supporting sintered particles of metal to substantially keep pace with the wear that in order to obtain maximum efllciency as regards the above features the metals which provided. This annular member I has a surface 8 adapted to be fitted to an auxiliary support 9.

for'the tool, as illustrated in Fig. II, and is provided with an annular substantially central tongue iii which, as illustrated in Figs. III and IV, is provided with a plurality ofangularly disposed slots H. The tongue I0 is provided with a relatively sharp edge 12 and tapers outwardly from said sharp edge toward the main annular portion 1 thereof to substantially parallelly related curved channel portions l3 and I4. Each of said channel portions has outwardly tapering walls l5 and 16 providing relatively sharp edged rim portions encircling the central tongue H). The annular member 1 formed of mild machine steel or other solderable metal is adapted to become attached to the backing support 4 through a chemical and mechanical bond with the said mechanical bond resulting from the interlocking of the tongue I0 with the heat joined particles of metal forming the backing support 4. This interlocking being brought about through the outward and inward deflection of the relatively sharp edge ll of the tongue I 0 adjacent! the slots II by prior bending or by bending which takes place during the fabrication of the tool and also through the interlocking of the heat joined particles of metal of the backing support 4 within the various angularly disposed slots i 8. When in secured relation with the backing support 4 the annular member 1 maybe machined throughout its inner surface 58 to fit a central protuberance IS on the auxiliary support 9 and the bottom surface 8 of the annular member I may be joined to the auxiliary support 9 by soldering or the like. It being understood, of course, that the engaging surface 8 and adjacent surface of the portion 9 are machined so as to suitably fit each other prior to said soldering operation. The central protuberance l9 interfitting'within the annular recess of the main portion of the tool provides means for centering the tool with the auxiliary support 9. This is brought about by forming the peripheral contour of the protuberance concentric with the axis 2| of the auxiliary support 9.

In forming the tool illustrated in Figs. I and II the annular member 1 is supported on a sleeve 22 mounted within a tubular member 23, in a casing 24. .A central arbor like member 25 is placed within the sleeve 22 and extends upwardly through the annular member I. The members 22, 23, and 25 are preferably formed of a hardened steel with the casing 24 formedof a relatively soft steel. The portion of the arbor-like member 25 extendingupwardly through the annular member I is spaced relative to the innerwall of the tube 23 and controls the thickness of the wall of the backing support of the finished tool. Particles of metal 26 of a suflicient amount to form the backing support 4 are placed within the space between the arbor-like member and tube 23 above the annular member 1 with the said particles being arranged to substantially the same level above the annular member 1. A liollow plunger 21 having a preformed face 28 of the shape desired of the interface 3 is placed in the die formed by the parts 22 to 25 inclusive and the assembly is then placed in a press 23. This press 29 may be of any suitable known type. For ease of illustration there is shown a press comprising a base plate 30 having uprights 3i thereon on which a second plate 32 is slidably supported. Suitable compression springs 33 normally urge the plate 32 in a direction away from the base plate 30. Suitable stop means, such as nuts 34, limit the upward movement of the plate 32. The die members 24 and 21 having the annular member 1 and material 26 to be compressed therein is placed between the plates 30 and 32. A plunger 35 slidably mounted in the casing 35 is forced downwardly by hydraulic pressure or the like or through compressed air directed through an inlet 31 into a chamber 38. It is to be understood that the above press and function thereof is given only by way of illustration. For example, instead of the pressure being exerted only from one direction-the pressure may be applied in an upward and downward direction or, so as to produce a reciprocal pressure, simultaneously, or the dies may be arranged to float under the action of pressure. In any event the arrangement should be such as to tend to bring about an equalization of pressure throughout the mass. The pressure exertedon the metal particles26 depends of course upon the nature and size of the metal particles used. In this instance, the metal particles preferably comprising approximately 16.5% of copper and 83.5% of chromium of approximately from 200 to 325 mesh. The copper and chromium are of substantially the same mesh and are preferably thoroughly mixed in a suitable tumbling machine or the like for a period of approximately twelve hours or for a duration sufficient to completely mix theparticles with each other. The plunger 21 is placed under ,a pressure of approximately 20 tons per square inch causing the particles of the mixture 25 ofth e copper and chromium to be compressed into relatively intimate relation with each other and with the parts of the annular member 1 and to causethe upper edge thereof .to assume the shape of the face 28 of'the plunger 21. The plunger 21 is then removed. Particles of abrasive of a desired mesh ranging between 80 to 115 or other suit-able mesh depending upon the working characteristics desired and. metal particles comprising 16.5% of copper and 83.5% of chromium are thoroughly mixed in a tumbling machine or the like fora-duration suillcient to substantially equally distribute the. abrasive particles in the metallic particles. It is also tobe understood that the proportion of the abrasive to a the powdered metal is varied according to the abrading characteristics desired of the tool. By increasing the amount of abrasive particles the abrading function of the tool is increased and' vice versa. This mixture of particles of metal and abrasive such as set forth above is then placed in the mold as illustrated at 39 in Fig. VI ;-g b2! the compressed partides 26 which form the backing support 4 and are preferably levelled oil. in said mold." It-being understood, or course, that the proper proportion of the mixture 26 is controlled to produce the size of backing supp rt 5 4 desired. The proportion of this mixture of particles of metal and abrasive is sumcient to produce the effective abrading layer l of the tool. The interface .3 formed by the shape 23 of the end surface of the plunger 21 is preferably first dusted with a copper powder just prior to placing the mixture 33 in the mold. A plunger 40 having an end surface 4| of the shape desired on the surface-2 of the abrading tool is then placed in the mold and'the a press 29 and a pressure of approximately 60 tons per square' inch is then applied. The compressed assembly including the annular member 1 is then removed from the mold and placed in a suitable furnace and heated to approximately 2500" F. 20 for a duration of approximately 5 minutes. This heating is preferably formed in theabsence of oxygen to prevent burning, scaling and so forth of the material during the heat treatment. This may be accomplished in many different ways.

25 By way of illustration the compressed assemblies designated 42 in Fig. XIV may be placed in a container 43 containing coke dust or the like 44 which completely surrounds the assemblies'42.

container 42 and is sealed on with a high temperature cement 46. 'The said cement can be 5 produced by combined fire .clay and cement or may be of any other desirable cement of the type which withstands heat. The packed container 43,

including the coke dust and assemblies 42, are

then placed in a suitable furnace diagrammati- 40 cally illustrated at 41, in Fig. XV, at approximately room temperature. comprises a heat chamber 43 having a suitable heating unit 43 therein and having a closure member 50 adjacent one end thereof by means of which the container may be inserted or removed from the furnace. The temperature of the. furnace is raised to approximately 1000 F. in approximately 70 minutes. The temperature is then slowly raised to approximately 2000 F. throughout an interval of approximately 50 minutes and is held at said 2000 for approxi-. The temperature is then mately 30 minutes. raised to approximately 2500 F. over a period of thirty minutes with the total heating time approximately three hours.

The heat is then shut off at the end of the time interval set forth above and allowed to cool down to room temperature from theapproximate high temperature 'of 2500 F." 0f course, it .is' to be understood that the 'temperatures and time may i be varied-according "tothe size-of container 43, amount of coke used, etclyand desired degree of hardness' of the resulting The coke ,dust is preferably used for the purpose'of absorbing the oxygen content in the air and functions as "axle oxidizer to prevent burninga: the materials,

scaling,'etc'. and to properly bond-the metalpare ticles. Hydrogen, carbon monoxide or any other deoxidizing agent might be used instead of coke dust. In this particular instance the furnace of the type illustrated diagrammatically in Fig. XVI might be used. The furnace in this instance comprises 'a-chamber 5| having a plate 52 on which the tool assemblies 42 are positioned. A controlled flow of a desired deoxidiz embly is placed in the The said furnace ing agent is directed through an inlet 53 through the chamber and thence outwardly through an outlet 54. Any suitable heat generating means 55 may be used under the chamber 5i to'heat the assemblies '42 to desired temperature. By reason of the fact that there is a continuous fiow of a de-- oxidizing agent through the chamber 5!! the oxygen is driven off and the heating takes place without danger of burning or scaling, etc., the assemblies that are being heated thereby creating a complete bonding of the metal particles.

If desired, the assemblies 32 may be subjected to a temperature of 2500 F. for a'period of 5 minutes in a controlled neutral atmosphere. In this latter instance, the heated assemblies are directly removed from the furnace and quenched in oil or subjected to other suitable treatment for hardening such as by a comparatively slower cooling in a deoxidizing atmosphere. The tern-w perature and time interval of heating of course is controlled according to the degree of hardness desired. The desired degree of hardness ranges between 68 to 82 as read from a scleroscope. Of course, the degree of density of the tool may be controlled by the size of the metal particles, amount of pressure and heat used during the tabrication of the tool. The tool resulting from the above assembly, as illustrated in Fig. II, is preferably the combined portions 9, 4i and l with the portions and i bonded together through an alloying which takes place throughout the inter;- face 3 with the portions 3 and 5 having a combined mechanical and chemical bond. The mechanical bond being insured through the provision of the slottedcircumferential tongue it which extends within and is anchored through the heating and sintering process internally of the backing support 1;. The annular member 71 being of a mild machine steel or other solderable metal will naturally be muchsofter than the metal of the sintered backing supporter effective abrading portionv l of the tool. The metals set forth above for said portions I1 and 6 result in a composition which has relatively non-solderable characteristics. It is very hard and dificult to machine. Through the use of an auxiliary annular member 1, such as illustrated in Fig. H, means aesaaro mately 5% copper in the mold as illustrated in Fig. IVIII; the said mold being formed in a manner similar to that of the mold illustrated in Fig. V. The layer 56 is levelled off by suitable means and a relatively thin bushing 51 is then inserted over the central arbor-like member and a spacer sleeve 58 is inserted between said arbor and sleeve 51 to hold said sleeve in position. The lower end of the sleeve 59 engages and if desired may be slightly embedded-in the layer of metal particles 56. A suitable proportion of a mixture of metal particles 60 of approximately 16.5% of copp r and 83.5% of chromium is placed in the mold as illustrated in Fig. IX between the sleeve ill and tube 23 of the molding die. The amount of the mixture to placed in the mold depends upon the thickness of the backing support iii desired in the completed tool, such as illustrated in Fig. XIII. The spacer sleeve 58 is then removed and a deposit of metal particles of the mixture of approximately 95% cobalt and 5% of copper is then placed between the relatively thin sleeve 57 and the arbor 25 as illustrated at 62 in Fig. X. It is particularly pointed out that the deposit t2 engages the deposit 56 as illustrated at 63. The relatively thin sleeve 51 is then carefully removed to allow the particles of metal of the mixture to to move into engagement with the particles of metal of the deposits 56 and 52.

is provided which may be easily machined so that a the said annular member may be fitted to the protrusion is of the auxiliary" support 9 and the engaging surfacesof said annular portion '0 with the portion may be joined by soldering as illustrated at 2B or by other bonding means. It

is apparent that the said annular member i may be increased in thickness so that mechanical binding means, such as screws or the like, may be used to anchor the said abrading member to the auxiliary support 9. The'auxiliary support 9 is provided with a tapered recess by means of which it may be attached to the spindle of an abrading machine. The tapered opening of course is 'co-axial with the axis M of the tool and the abrading element is also co-axial withsaid axis. V 1

It is to be understood that although applicant has shown and described an abrading tool of an annular type other shapes of abrading surfaces may be formed as desired. I

.Referring now to Figs; VIII to XIII inclusive 9. modified form of tool may be formed by placing a layer of metal 58 of a mixture of approximate- 1t 95% of either cobalt, iron,"nickel or metal'or combination of metals of a high melting point that is solderable and machineable and approxi- The plunger 2'l having the preshaped end surface 28 thereon of the shape desired of the interface 6d of the tool illustrated in Fig. XIII is then placed in the mold as illustrated in Fig. XI. The assembly is then placed in a suitable press such as illustrated in Fig. VII and the particles of metal are pressed into adjacent relation with each other. The pressure in this particular instance is approximately 20 tons per square inch, it being understood, of course, that the deposit M has been previouslylevelled ofi prior to said compressing. The plunger 21 is then removed and a suitable amount of a mixture of metal particles such as set forth above for the deposit 5i! and containing abrasive particles such as crushed diamonds, sapphires or the like is then placed in the mold, as illustrated at 65. The interface 64 is preferably first dusted with copper powder prior to placing the deposit 35 in the mold. The

deposit to in this particular instance comprises approximately 38 grams of the mixture of chromium and copper as set forth above with approximately 8 k. of diamond particles of a desired meshdepending upon the type of tool. desired. The plunger fill having an end surface M thereon of the shape desired on the eflective abrading surface of the tool is then placed in the mold and a pressure of approximately 60 tons per square inch is applied. This pressure is preferably applied with the members'22 and 25 protruding below the members 23 and 24 when the assembly is placed in the press 29. v

The resulting compressed assembly is then removed from the mold andheat treated by any one of the heat treatments set forth above Preferably the slow cool method. The amount of the deposit 65 is controlled so as to produce the desired finished thickness of the effective abrading portion 56 of the tool.- In the resulting article a the layer 55 and layer produced by the deposit 62 will have a bond throughout its contiguous surface 61 with the backing support 6|, of the tool. The bond is essentially brought about by the interfitting ofthe particles of the layers 56, 52 and SI through an inherent irregularity which results 7| from the removal of the relatively thin sleeve 51 an interval of approximately 30 minutes. tool is then allowed to cool down to room temfrom the mold. The bond may be increased by relatively hard and resistant to wear with the degree of hardness such that the said eifective abrading surface will not scale over and reduce the effectiveness of the abrasive particles held by said layer. The hardness is preferably such "that the wear of the bonding material of the layer will substantially keep pace with the wear of the abrasive particles so as to insure their performrnaterial of they ing to the fullest extent of their usefulness prior to their being dislodged from the tool.

Other mixtures of particles of metal for use as the bonding material for the abrasive particles and for the backing support of tools of the character set forth abovemay be formed as follows:

A. A mixture'of approximately 50% of chromium plus approximately 50% of copper or the copper may be reduced to approximately combined with 95% chromium depending upon the resultant hardness and working characteristics D of approximately 16.5% of copper and 83.5% of chromium may be used as previously set forth above in which instance the hardness reading will be from 50 to 75 as taken by a scleroscope depending upon the hardness desired. Of course thehardness may be of any controlled amount ariived atby' controlling of pressures and heat treatment. It has been found that it-is preferable to have different degrees of hardness for use with difierent types of glass or other material to be abraded as well'as diiierent grinding applications. This is oneof the most preferred mixtures for use in forming the backing support and bonding means for the abrasive particles.

' The various different mixtures of particles'of metal for forming the backing supports and bonding means for theabrasive particles of the tools .may be compressed and heated according to the degree of density desired, hardness and resistance .to wear desired and, of course, the said pressures and temperatures will have to be varied according v to the particular mixtures of metal used. The heating may be accomplished by any of the methods set forth above or by any other known means of heating under deoxidized conditions. If. a mixture of approximatelv- 16.5% of copper and 83.5%

of cobalt were used,'of course, no auxiliary solderdesired. The greater amount of chromium used the greater hardness and wear resistance the tool will have. The resultant hardness is controlled by the temperature andpressure used in, fabricating thetqol. r

B. A mixture of approximately '50 to 50% of nickel, approximately 30 to 45% of copper and approximately to of tin, with the latter. mixture a pressure of approximately 17 tons per square inch is applied to the particles forming the backing support of the tool. .The pressure applied to the assembly when the mixture of bonding material and particles of abrasive are placed in the die to form the efiective abrading portions I or 66 of the tool as the case may be is approximately 35 tons per squareinch and a heat temperature ranging between 1600 to 1925 F. is used with the temperature of 1600 being raised from room temperature throughout an in-- terval of from approximately 60 to 80 minutes.

The temperature is raised slowly to approximately 1700 F. throughout an interval of 50 minutes and is held at 17 OO F. for approximately minutes and then raised again to between "1725 F. to 1925" F. This takes place throughout The square inch is used and a heat treatment of approximately 2500 F. is used for a period of 5 minutes, The tool may be cooled either by quenching or slow cooled preferably in controlled atmospheres. In all instances to insure bonding throughout the interfaces 4 or 54 ofthe tools, as the case may be, the said-interfaces are pref 'erably dusted with copper powder during the fabrication of the tool. A tool formed by the mixture of approximately 16.5% of copper and 83.5%

of cobalt has a hardness of approximately 20 as obtained from average readings of a scleroscope.

Of course. it is-to be understood that a mixture able layer such as illustrated at l or 56 would be necessary as the'material of said mixture will readily solder with the auxiliary support. This is also true if the mixture of nickel, copper and tin is used, such as set forth above. The preiliary support 9, a solderable metal such as set construction of the annular member I may be mechanical bond;

forth for the annular member I or for the layers 56 and 62 may be used. The said solderable metals used for said annular member I and layers.

56 and 62 are" of such a nature as to have to a greater extent a mechanical bond and to a lesser extent a chemical or alloying bond with the metal of the main tool portion.

In the construction, illustrated in Fig. II, more of a mechanical bond exists as is intended by the particular construction of the annular member 1 used. It is to be understood that the details of varied in order to produce the desired type of This one particular design being shown and described only by way of illustration. It is to be understood that the mesh of the particles of metal used for the various different layers may be substantially consistent with the mesh set forth for'the 16.5% of copper-and 83.5% of .chromium mixtures set forth above.

Grinding tools or laps, as commonly known in the ophthalmic art and as: formed according to the present invention, are intended for various diflerent types of grinding or abrading. It is therefore in'accordance with the present invention to .provide toolsor laps which are particularly adaptable for the particular use to which they are to be put. This, therefQre means that for one-type of grinding a tool of a different hardness may be used than for another type of grinding and yet obtain the desired speed and emciency of grinding. A tool for said particular grinding has the desired durability and effective ness. The invention, therefo'rals intended to cover all different types of tools with different degreeswof hardness and wear resistance according to the pressure and temperature controls used in; fabricating the tool and of the particular compositions of meta] used for said tools, in accordance with the teachings of the present invention.

' From the foregoing description it will be seen that simple, elflcient and economical means and methods have been provided for accomplishing all of the objects and advantages of the invention.

Having described my invention, I claim: 1. \An abrading tool having an abrading portion comprising particles of abrasive mixed with and held by particles of metal which metal particles Y are heat joined with each other, said particles of metal comprising a mixture of copper and chromium with the chromium being of 'a greater amount than the copper and the copper content being of an amount which is sufficient to bond the chromium and the abrasive particles to a coherent mass and a backing support for said abrading portion comprising an intermediate part of metal of characteristically the same mixtui-e as that of the abrading portion having a portion ofmetal of a solderable and machineable nature bonded therewith.

2. An abrading tool comprising a mixture oi abrasive particles dispersed in a body portion oi a mixture of copper and chromium particles heat joined with each other to retain said abrasive particles therein, the chromium particles being in excess of the copper and the copper particles being of an amount which when heat joined is sufficient to bond the chromium and the abrasive particles into a coherent mass.

3. An abrading tool comprising'abrasive particles and a sintered metal bond comprising an alloy of from 5 to 50 per cent copper and from 50 to 95 per cent chromium.

4. An abrading tool comprising a main abrading portion of particles of abrasive, mixed with a slntered metal bond comprising arr alloy of copper and chromium with the chromium in excess of said copper and with the copper vloeing of an amount which when the particles are sintered is sufficient to bond the chromium and the abrasive particles into a coherent mass, said abrading portion of the tool having a preshaped abrading surface on one side thereof and said sintered metal having a solderable metal bonded thereto on the side. thereof opposite the abrading surface JOSEPH T. KELLElZ-mt. 

